In a standard liquid dispenser, a liquid is pumped by one of many means. Particularly for liquids containing a coarse grit material, the method of pumping is with a diaphragm pump, tube pump (where the tube is compressed to seal then push fluid out), and piston pumps.
In some situations, accurate measurement of liquids is desirable when dispensing the liquids. Too little liquid may be insufficient to sanitize the object receiving the liquid. Too much liquid is wasteful and increases cost. Standard liquid dispensers do not provide an accurate means of controlling the amount of liquid that is dispensed. In diaphragm and tube pumps, the pumps swell as they are being compressed which allows some of the fluid in the pump to remain, resulting in pumps that are inefficient at controlling the volume of fluid. Even with dosage control mechanisms, the pumps cannot consistently deliver an appropriate amount of liquid. Piston pumps do not effectively deliver grit soaps because the piston/cylinder assembly wears unpredictably and may leak or not pump efficiently.
Finally, bag-in-box type fluid reservoirs, which have some form of plastic liner and cardboard exterior package (bag-in-box), do not evacuate efficiently because the bag can fold on itself and trap fluid not allowing it to be pumped from the bag.